The industry of the manufacture and conversion of corrugated board employs machines known as slitter/scorers that slit a web of continuous material into a plurality of strips of smaller width than the width of the web, and that also produce score lines on said strips, that is to say lines preparatory to the subsequent folding of the material.
U.S. Pat. No. Re. 35,345 discloses a slitter/scorer machine in which each slit line is produced by two disk blades pressed against each other. In U.S. Pat. No. 5,090,281 each slit line is produced by a blade rotating at high speed and working in conjunction with an opposing roller with an annular channel into which the blade enters. The opposing roller provides support for the web during slitting. U.S. Pat. No. 5,406,869 discloses a system in which the web is supported by a flat surface over which the web travels. The flat surface contains a longitudinal groove into which the blade passes and a series of holes through which air is blown to create a cushion of air on which the web is supported.
In JP-A 8-164572, besides the solutions described above, an account is also given of a machine in which the slitter blades work in conjunction with brushes situated underneath, and the board passes between the blade and the brushes. This method has the disadvantage that the blades damage the brushes, making it necessary to replace the brushes at frequent intervals.
In the manufacture of sheets of board slit and scored from continuous webs, the format and therefore the position of the slit lines and score lines has to be changed frequently, since the machinery does different jobs requiring different sheets in rapid succession. It is for this reason that slitter/scorer machines with two in-line series of scoring tools and two in-line series of slitting tools are used. This makes it possible to process one sheet job on one series of scoring tools and slitting tools, while the other series of scoring and slitting tools is positioned by robots for the processing of the next job. Since the slitting tools usually include, for each slitting line, one blade and one counterblade, it is necessary to employ two positioning robots, one for the blades and one for the counterblades.
This makes the machine complicated and expensive.
Other examples of machines for slitting and scoring webs of corrugated board or similar materials are disclosed in EP-A-0 541 953, EP-A-0 607 084, EP-A-0 692 369 and EP-A-0 737 553. All these machines provide a counterblade for each slitting blade.
In all the slitting devices in which the slitting tool operates in conjunction with an opposing channel, formed in rotating counterblade or in a surface or in the form of supporting brushes or fingers, there is the additional disadvantage that the web undergoes deformation along the line of penetration and exit of the slitting tool from the underside of the web: what happens is that at the point at which the slitting tool emerges from the underside of the web, the web tends to be pulled down by the sides of the slitting tool into the channel below. This produces an irregularity in the edge of the line where the web has been slit, especially where the web is corrugated board.